Generally, network traffic for a connection between two nodes is carried on a transmission link. Additional links are used to support additional connections. The transmission media for each link may be fiber, copper, or other transmission media. For example, when optical link is used, new fiber lines are used to accommodate additional connections. FIG. 1 is an exemplary illustration of multiple fiber connections between two switches. The eight ports in the switch 105 on the left side are connected to the eight ports in the switch 110 on the right side. While the approach of adding more connections and using more ports works, it is expensive. As the demand for bandwidth increase, there will not be any ports left to add new fiber connections.
Advance in network communication allows multiple connections or channels to be a single physical link. For example, Wavelength Division Multiplexing (WDM) is a technology that allows a single optical fiber to support multiple optical channels. WDM uses multiple lasers and transmits several wavelengths or colors of light (lamdas) simultaneously over a single optical fiber. FIG. 2A is an exemplary illustration of transmitting multiple signals using different wavelengths. Each wave length or channel travels within its unique color band, which is modulated by the data (text, voice, video, etc.). WDM systems (also referred to as DWDM systems) are capable of supporting multiple wavelengths. One wavelength is sufficient to transfer a 622 Mbit/s (OC-12), 2.5 Gbit/s (OC-48), 10 Gbit/s (OC-192), or 40 Gbit/s (OC-768) signal.
FIG. 2B is an exemplary illustration of DWDM using a single fiber. DWDM is important because it enables a single optical fiber to carry many times the amount of network traffic it could not otherwise. Signals from the different ports of the switch 205 are transmitted at slightly different wavelengths of light. These signals are multiplexed so that they can travel together on one fiber 220. At the other end of the fiber, the different wavelengths are separated, and the signals recovered by the switch 210. Thus with DWDM, upgrade costs can be reduced.
With DWDM comes a challenge of figuring out how to manage all of these high capacity channels running in parallel in a single optical fiber.